I was listening to livecast on youtube the other day. And the host mentioned about Finality implementation every 20 blocks or so.
Can someone epxlain for why do we need finality or locking the blocks? I understand that it is for making the blockchain irreversible. But as every block number is function of time (especially in PoS, where there is no delay in block generation like PoW), every block is anyway final. If a miner is trying to add a block at a blocknumber whose time has passed, miner won't succeed.
Is my understanding correct?